Large diameter chord members employed in such structures as large towers and particularly offshore oil platform support jackets are subjected to a wide range of tensile and compressive stresses. Such stresses are particularly concentrated at points where bracing and crossing tubular members engage the side walls of the chords. At these points, tension and compression forces acting along the attached bracing members can act to buckle, punch or fatigue crack the side walls of the chord members. In the past, several means of internal reinforcement for the chord members have been employed. The overall effect of such reinforcing is to distribute tensile and compressive forces transmitted by bracing members over a larger area of the chord wall.
The most common reinforcing structure for chord members is a series of internally positioned ring structures welded to the inner walls of the chord member in the area at and adjacent to the intersection of a bracing member. Commonly, several rings are employed at spaced intervals in the area of an intersection. The weight, complexity, and cost of the complicated, multistep welding process makes such a stiffening system a disagreeable choice. Further, the generally radially oriented reinforcing rings do not effectively distribute forces acting against the side wall of the chord structure when the bracing members intersect at an angle other than perpendicular to the chord wall such as in a so-called K- or X-joint.
U.S. Pat. No. 4,130,303, describes the reinforcement of a pipe cross fitting for interconnecting tubular structrural members in which plate members are disposed diametrically across the internal diameter of the intersecting structures. Tension and compression forces are concentrated at the welds at which the small abuting areas of the plate members intersect with the chord walls.
Other prior means of reinforcing tubular structures include radial web walls as described in U.S. Pat. No. 2,196,708 and crossing wooden beams which engage the inner walls of a tubular member such as described in U.S. Pat. No. 3,776,253.
None of the foregoing prior art reinforcing systems effectively distributes tensile and compressive forces acting against the side walls of a chord member at an intersection with a bracing member of the complex joint. For the purposes of this specification, a complex joint is defined as an intersection of a chord and bracing member at an angle other than perpendicular to the major longitudinal axis of the chord member.